As a rule minimum payments are required during promotional period. You will be given a chance to pay off the balance during promotional period without paying the interest. If you are not paying the minimum or late with minimum payments, your 0% interest promotional APR will turn into penalty APR and the interest will accrue. Plus the issuer may charge you a penalty fee for the late payment.
The minimum payments are determined by the issuer and depend on your balance. The issuer should inform you what minimum payments you should pay and about the payment due date.